What Is HL7 v2 NK1-5? Phone Number, Explained for Testers
An emergency contact number that a nurse can't dial because a stray extension code corrupted the number is the kind of NK1-5 bug that never shows up until someone actually needs to place the call.
NK1-5 holds a phone number for the associated party using the extended telecommunication number (XTN) data type, which can bundle a plain formatted number together with structured components like area code, local number, and extension. In practice, most sending systems only ever populate the free-text first component.
What this field contains
Example
The synthetic value 3035550142 is a plain, unformatted ten-digit number in the free-text component of NK1-5.
Where this trips people up
Because most real-world traffic only fills the free-text component, code that expects area code and local number to be broken out separately fails silently and falls back to an empty or malformed display. On top of that, formatting is inconsistent across sending systems — with dashes, without dashes, with a leading "1," or with international prefixes — so test coverage limited to one clean format will miss the reformatting bugs that show up the moment a second source system is connected.